In the laboratory, you are studying TrbL, a 70 kD protein that causes tribbles to be furry. You isolate a 70 kD protein that you believe to be TrbL using gel filtration chromatography. When you run your sample on an SDS-PAGE gel and stain with Coomassie, you observe a single band at 70 kD. To determine the sequence of the N- terminal region of the protein, you carry out several rounds of the Edman degradation. Unfortunately, the first round suggests that you have both alanine and tyrosine present. The second round tells you that you have both tryptophan and valine present. In fact, each of the rounds of the Edman degradation suggest that two amino acids are present.
a. Assuming that your protein sequencing apparatus is functioning correctly, suggest a simple explanation for your result.
b. Give a simple experiment that will allow you to test your answer to part a.
c. How would you test your protein sequencing apparatus to be certain that it is working correctly and that your difficulties are specifically associated with your sample of 70 kD protein?